Fig. 2

Adhesive force measurement a; Sample having a constant volume of 0.1 ml is squeezed between two stainless steel disks (diameter, 35 mm; thickness, 1 mm). Thickness of the sample between disks is maintained by 2 layers of scotch tape stuck on the bottom disk. b; Sample is immersed in artificial saliva, and shaken at 37 °C at 37 rpm (1, 2, 3, 4, 5 or 6 h). c; Bottom disk is firmly fixed to a glass disk, while a hook is fixed to the top plate using glue. A portable hanging weight scale is hitched to the hook on the top plate, and the hanging scale (see Additional File 2.) is pulled. Normal force caused by sample adhesiveness is measured